Heat-treatment of copper-nickel-manganese alloys



Jan. 17, 1950 D. R. HOOD ET AL HEAT TREATMENT OF COPPER-NICKEL-MANGANESE ALLOYS 4 Sheets-Sheet 1 Filed Aug. 2, 1945 ON M N W mm 0v m v um mm e2 50 o 9, wwiilii Y J B wmlwz ATTORNEY Jan. 17, 1950 D. R. HOOD ET AL HEAT TREATMENT OF COPPER-NICKEL-MANGANESE ALLOYS 4 Sheets-Sheet 2 Filed Aug. 2, 1945 7valNVENTORS" TTORNEYS BY vii/Maul,

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INVENTORS.

ATTORNEYS.

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Patented Jan. 17, 1950 HEAT TREATMENT "OF 'COPPER NICKEL MANGANESE AL'IIOX'S Donald-.3: HOQd:, sl1d Stanley R..Hod, Llletroih. Mich-.,.assi;1o1s,. by mesne assignments, to Chi- .cagrn Development Company; Chicago, 111;, a corporation oflllli'noiw ApplicatiomAugust 2, 19:15., Serial:No;@60s8,440

6 Claims.

This;inventionrelatesstol-improvementssin heat treating ;pr,ocedure-.-torecopper-niokelvmaln ane alloys such as: are de cribed-in Patents-l No. 2,234,552,.and 1N0; ,2,-270,,868.-.'. The alleys: of these patents, which -,-seem-- 1101 116 of most:- commercial importance; at the present time containtime-75% copper, with the:remainderrsubstantially: equal parts of nicketandmanganese- We haves-found bycmodifyingntemperaturessandyratesaoftemperaturenhange: heat-treated alloys cam be made. with improved physical-.zprpperties, which lrequire less time: for? developingghairdnesssand do nc-t: require an objectionable;highsolutioniemperaturetreatmentpreliminaryetoehardening;

Patent No. 2,234,552, referredqtocabove;specifies quenchingxrthezalloyscfnom 9.009 6. or-"highersand statesfurtherrthatiiffaelower onermhing temperature is used; ,thea-finai rhardening :orraging:- step will be-zless-zeffectivee .snchuaestatementncan'zbe made in' reierenceto precipitationzhardeningi alloys generally', that ls; therevis: aeceetainxminimum temperature from quenching: must: take place :tomaintain a supersaturated solution from which a constituent maytsubsequentlysbeprecipitated by heating thealloyibelowt the. quenching temperature; We haveiound not only does such a procedure-notapplyto-these'eflloys; but; in fact, the opposite is true; namely, the farther below 900 C. quenching'takes place, themore effective the aging-treatment; The only limit'in decreasingthe quenchingtemperature is'theoverlapping'of the aging temperature-range.

Even ,further -removedfrom-"tl'ieusual precipitationhardeningprocdure"is the-insensitiveness of these alloys to rate of cooling from the quenching temperature. Ordinarily it necessary to cool rapidly from the solution temperature to maintain a highsolubilityyof the-precipitate in the alloy. We have foundtheseallbystoharden through amentirely difierentimechanism. The alloys maybe water quenched, a'ircooled, or even furnace cooled without" appreciably changing either the maximum-hardness"whichtmay beproduced or theztime required foraging.

.21 Thatsuch an insensitiveness to cooling rate is 'nQtzdque..to mere.. sluggi hness ofjthe o but adifferent hardeningmechanism is. shownby its reversible? heat treatment. Wehave found that hardening and softening can: be. alternately prod-ucedby temperatureechang-es without the .in-

termediate; quenching.- or solutionv step.

In'the clrawingsi Fig; 1 shows thera-nge iover-rwhichxthecoppernickel-manganese alloys of our invention are hardenable. InF-i'gs. 2 toz6 the;=graphs relate'to an alloy containing-60% copper, 20%-mcl el; and 20% manganese. It will benoted "that Fig; 1 -correspondsto Fig; IoFPatent-No. 223435-52 and; as insaid patent, theshaded"or cross-hatchedarea representsthe hardenable range ofthe alloys. Thedotted arearepresents alloys which are hard as cast, are not=easily fabricated;- anddo notfall "Within the ,scope..of,.the presentinvention... The line MnNi substantially bisects the=shadedrarea and correspondsswith. the. hypothetical compound Fig: IZ'ShOWS the-effect of: solution temperature onthe :hardenabili-tw offsuchalloy.

Fig; 3' 'shows'the'xeffect goftimeat solution temperature-onthe hardness of such-alloy.

Fig; 4 shows the efifect'of solution'temperature on the time-hardness curve.

' Fig. 5 shows the time hardness :curve'for such alloy.

Rig. 6 shows the:effect-of-'-time-at solution temperature on thetime hardness-curve ,forsuch .35 alloy.

Eig. 2,.shows the, efiect of solution, temperatureaon .the hardenability of an alloy, containing 60% copper, 20% nickel, 20% manganese. Samto fifty-sixhours. Thisissampletime for most of theaging tmtaKeplacegdn-all samples. The

hardness; grain: size,-v and: tensileproperties: are

tabulated*forzfullyzhardenedsamples :havingvariens-solution temperatures aszfollows:

pleswere aged-at 7502 for/periods oiltimenup .tests on production parts.

the final forming and aging operations.

' time. reheated above the optimum aging temperature,

only is the hardness increase less pronounced for 1 th samples having high solution temperatures, but the rate of hardening is much slower. Fig.

3 shows the drop in hardness of cold rolled sam-' pies after being heated to 950, 1000, 1050, and 1100" F. for time intervals of /2, 1, 2 and 4 hours. It is shown that 1000, 1050, or 1100 F. may be used with approximately the same drop in hardness resulting. At 1100 F. full softening takes place in less than /2 hour. At 1050 F. slightly longer heating is required, and at 1000 F. over one hour at temperature is required. At 950 F. a remarkable phenomenon occurs in that both softening and hardening occur at the same temperature. At this temperature the hardness first drops, probably due to relief of cold work stress, and then as the metal remains at this temperature, aging begins and the hardness increases.

-This makes it possible to 'give a stress relieving heat treatment prior to the aging treatment. Such a treatment greatly decreases distortion during aging. This has been verified by actual The material can be stress relieved either by heating the metal in a continuous strip or strand annealing furnace, or blanked elements may be stress relieved before This stress relieving step does not appreciably affect either the subsequent hardening rate or the physical properties as compared to rolled and aged material.

Probably the most useful characteristic of the heat treatment of these alloys is the discovery of their reversible hardening. Generally, precipitation hardening alloys harden most rapidly by using as high an aging temperature as possible. If, however, the temperature used is too high, resolution of the precipitate occurs, and it is not possible to obtain full hardening without repeating the quenching treatment and reaging at a lower temperature. We have found the copper-nickel-manganese alloys to follow an entirely different heat treating pattern. These alloys have most rapid hardening and obtain maximum hardness at an intermediate aging temperature. Using a higher temperature increases, rather than decreases, the hardening If, however, a fully hardened sample is the hardness is drawn to a lower value, depending on the drawing temperature. By selecting the temperature correctly a fully hardened sample can be drawn to any hardness between full hard and dead soft. Within practical limits this drawing depends only on temperature and not on time. The time at temperature may vary between one-half hour and two hours without affecting the hardness drop appreciably. The unique feature of this drawing, however, is that full hardness may again be developed by merely heating to the normal aging temperature. Fig. 4 shows the temperature-hardness relation in drawing 60% manganese, copper, 20% nickel alloy. It will be noted that for annealing temperatures of 1000, 1050, or 1100 F. the hardnesses are substantially identical after ten hours of aging. It is interesting to note that even the slight differences in annealing temperatures in the range 1000-1100 F. show corresponding differences in hardening rates, that is, in the first six hours most rapid hardening occurs when the lowest possible annealing temperature is used. Although the grain size for samples annealed at 1000, 1050, and 1100 degrees is all very fine, there is a measurable difference the finest grain, of course, occurring at the 1000 degree anneal.

Fig. 5 shows the time-hardness curve for a sample of this alloy. Instead of reaching a peak hardness and then softening on further heating at the same temperature, this alloy shows no hardness drop after thirty days at the optimum aging temperature. The hardening effect is cumulative, that is, the hardening which occurs in a ten hour period is exactly the same as that which would build up in ten separate cycles of one hour each. From these characteristics it is possible to make heat treated elements with a minimum of variation in hardness. Any part which is not as hard as required can be reheated to the aging temperature for additional hardening. Any element which is harder than specified can be drawn back to the correct hardness. If elements already hardened require a change in form or machining as a result of change in design, it is only necessary to heat to slightly above the aging temperature to soften the material and after making the necessary alterations, reheat at the aging temperature to reharden. Local areas of hardened parts may be softened if desired.

As already stated, quenching in the ordinary sense of the word is not required as a prerequisite to hardening. The alloys may be furnace cooled and still age as well as a sample quenched from the same temperature. If cooling in the furnace takes place very slowly, partial hardening will occur as the metal passes through the aging temperature 'range. Therefore, the alloys can be hardened by iso-thermal heating, that is, merely dropping from the solution temperature to the aging temperature and holding at the latter until the desired amount of aging is accomplished. The commercial application of such a treatment is in the silver soldering of these alloys. Parts to be silver brazed may be run through a two zone continuous furnace in which brazing occurs in the first at a temperature which melts-the solder, and aging takes place in the second which operates at the aging temperature.

In the treatment of copper-nickel-manganese alloys outlined above, one starts with a cast alloy which has had its grain size substantially reduced by conventional methods such, a for example, as both hot and cold working or rolling, hot working or rolling from about 1650 F. down to room temperature or down to solution temperature and also cold working plus annealing. Hot rolling is used is softer.

of Fig. 1, the annealing temperature range is from about 975 F. to about 1300" F. with an. annealing temperature of 1050 F. preferred for the alloy comprising essentially 60% copper, 20% manganese, 20% nickel by Weight. The hardening temperature range for the alloy comprising 60% copper, 20% manganese, 20% nickel, or lesser amounts of manganese and nickel, is from about 500 F. to about 800 F. with a hardening temperature of 750 F. preferred. Where the manganese and nickel each exceeds 20%, the hardening temperature range is from about 500 F. to about 950 F. Where the manganese and nickel each exceeds 20% of the alloy or more than 40% together of the alloy by weight, the upper limit of the hardening temperature range is higher than for the alloy comprising essentially 60% copper, 20% manganese, 20% nickel. If the manganese and nickel each exceeds 20% of the alloy, or together exceeds 40% of the alloy, the higher temperatures in the above set forth annealing temperature range are preferably used. For example, an alloy comprising 40% copper, 30% manganese and 30% nickel should be annealed at about 1250 F. By annealing and hardening within the temperature ranges above set forth, an alloy having even better physical properties than those disclosed in the above said Dean patent can be obtained with substantially less cold rolling after annealing and before age hardening. In fact, with our annealin and hardening steps we can obtain a hardened alloy having better physical properties than those obtained by the treatment outlined in the Dean patent with only a 30% reduction in size of the ingot or casting by cold rolling between annealing and age hardening as contrasted with a 70% reduction in size by cold rolling between quenching and aging when Deans quenching and aging procedure is followed.

We claim:

1. The improvement in hardening coppermanganese-nickel alloys falling within the shaded area of Figure 1, which consists in working the alloy to reduce its grain size, then heating it to a temperature between 975 F. and 1300 F. to fully soften the alloy, cooling the alloy at a rate greater than that obtaining in ordinary furnace cooling and then heatin the alloy to a temperature of 500 F. and 950 F. for a period of at least hours whereby to obtain a hardened alloy with improved properties.

2. The method of claim 1 further characterized by cold working the alloy before heating to 500 F. to 950 F. to harden it.

'3. The improvement in the method of treating copper-manganese-nickel alloys, having 60% copper, 20% manganese and 20% nickel within the usual commercial composition limits for such alloys, which consists in the Working of the alloy to reduce its grain size, heating to a temperature of about 1050 F. for a period of at least 30 minutes to fully soften the alloy, cooling the alloy at a rate greater than that obtainin in ordinary furnace cooling and then heating the alloy to a temperature of about 750 F. for not less than 10 hours whereby to harden the alloy and improve the ductility of such hardened alloy.

4. The method of claim 3 further characterized by cold Working the alloy before heating to about 750 F. to harden the alloy.

5. The method of treating an alloy hardened according to claim 1 to partially soften then fully reharden it, which consists in the steps of heating to a temperature of 975 F. to 1300 F. for a period insuflicient to fully soften the alloy and then heating the alloy to a temperature of 500 F. to 950 F. for a period of at least 10 hours.

6. The method of claim 5 further characterized by cold working the partially softened alloy before heating it to reharden it.

DONALD R. HOOD. STANLEY R. HOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,816,509 Wise July 28, 1931 2,201,555 Corson May 21, 1940 2,234,552 Dean et a1 Mar. 11, 1941 OTHER REFERENCES Practical Metallurgy, Sachs and Van Horn, 1940, American Society for Metals, Cleveland, Ohio, pp. 123 and 124.

Age Hardening of Metals, 1940, American Society for Metals, Cleveland, Ohio, pp. 60, 61.

Transactions, vol. 34, 1945, American Society for Metals, Cleveland, Ohio, pp. 481-504. 

1. THE IMPROVEMENT IN HARDENING COPPERMANGANESE-NICKEL ALLOYS FALLING WITHIN THE SHADED AREA OF FIGURE 1, WHICH CONSISTS IN WORKING THE ALLOY TO REDUCE ITS GRAIN SIZE, THEN HEATING IT TO A TEMPERATURE BETWEEN 975* F. AND 1300* F. TO FULLY SOFTEN THE ALLOY, COOLING THE ALLOY AT A RATE GREATER THAN THAT OBTAINING IN ORDINARY FURNACE COOLING AND THEN HEATING THE ALLOY TO A TEMPERATURE OF 500*F. AND 950*F. FOR A PERIOD OF AT LEAST 10 HOURS WHEREBY TO OBTAIN A HARDENED ALLOY WITH IMPROVED PROPERTIES. 